Over the past twenty years, computer technology has evolved very rapidly. One aspect of this evolution has been a progressively growing demand for increased storage capacity in memory devices. In order to provide a high storage density at a reasonable cost, one of the most enduring techniques has been to provide a rotatable hard disk with a layer of magnetic material thereon, and a read/write head which is supported for movement adjacent the disk and can transfer information to and from the disk.
In an arrangement of this type, if airborne dust, smoke, vapors or other contaminants are present, they can be attracted to the disk or the head, for example by any electrostatic charge that may be present. Because the head is disposed closely adjacent the disk during normal operation, contaminants on the disk can be transferred to and progressively build up on the head. Eventually, the buildup of contaminants will be sufficient to interfere with the interaction between the head and disk, thereby increasing the error rate until the device will not operate. Also, if a large particle becomes trapped between the head and disk, it can cause damage to the magnetic surface present on the disk. Alternatively, such a trapped particle can cause stored information to be erased, without physical damage to the disk. In this regard, the particle can rub on the disk with sufficient pressure to elevate the temperature of the magnetic coating until magnetic information is thermally disorganized, or in other words erased.
In order to avoid these problems due to contaminants, most hard disk drives have the disk and head disposed within a sealed enclosure, so that the disk and head are not exposed to whatever airborne contaminants may happen to be present externally of the enclosure. This approach works well where the entire hard disk drive device is permanently installed in a computer. In other types of systems, however, a hard disk is provided within a removable cartridge, and it is desirable that the cartridge not include the read/write head.
In this regard, there are advantages to placing a read/write head and its support structure within the drive which receives the cartridge, rather than in the cartridge. For example, a typical user will have several removable cartridges for each drive. Thus, in terms of overall system cost, it is cheaper to provide one head with its support in the drive, rather than to provide several heads with supports which are each disposed in a respective one of many cartridges used with the drive. However, in removable cartridges, there is a problem in regard to keeping the head clean.
More specifically, in order to permit the head from the drive to access the disk within the cartridge, the cartridge is not provided with a sealed enclosure of the type discussed above. Instead, the cartridge is provided with an opening through which the head of the drive can be inserted into the cartridge. In some cases, a movable shutter is provided to obstruct the opening when the cartridge is not disposed in the drive. However, when the cartridge is disposed in the drive, the shutter moves to an open position. Thus, regardless of whether or not a shutter is present, when the cartridge is in the drive, there is an opening which gives the head access to the interior of the cartridge. That opening also necessarily gives ambient air access to the interior of the cartridge, along with any dust, smoke, vapor or other contaminants that are carried by the ambient air.
In order to reduce the incidence of errors, pre-existing systems of this type have typically taken the approach of using a relatively low density for the data stored on the magnetic disk. While this approach has been generally adequate for its intended purposes, it has not been completely satisfactory in all respects. In particular, and as discussed above, there is a progressively increasing demand for progressively higher storage capacities in devices of this type. To achieve this, there is a need to use higher data storage densities, which in turn presents an increased likelihood of errors in data stored on and retrieved from the magnetic disk.